This invention relates generally to motion producing apparatus of the electromagnetic kind. More particularly, it relates to a method of and apparatus for controlling movement of an armature in an actuator of the electromagnetic kind.
A wide variety of electromagnetic actuators exist. A typical motor or actuator is of the linear kind and includes a cylindrical bobbin about which is wound one or more field coils. Mounted within the bobbin is an armature. The armature may be comprised of a core formed from a piece of soft iron, as shown in U.S. Pat. No. 3,728,654, or it may be comprised of a plurality of permanent magnets, such as shown in U.S. Pat. Nos. 3,022,400, 3,202,886 and 3,495,147, or the armature may be a combination of a core and a permanent magnet. Through the application of direct current to the coil, a magnetic field is generated for facilitating production of a force sufficient for driving the armature in a given direction. Reverse application of the current polarity causes the armature to be driven in the opposite direction.
Another kind of linear actuator is disclosed in commonly-assigned U.S. Pat. No. 4,265,530, issued May 5, 1981, entitled "Shutter Blade Drive System", by the applicant of the instant invention. The described actuator represents an improvement over the kind mentioned above because it returns the armature to an original or central position upon deenergization. While such a linear actuator is extremely successful for the purposes intended, it nonetheless is limited to producing movement along a linear path. U.S. Pat. No. 3,320,445 discloses a pair of juxtaposed thin flat magnets and a coil with its axis transversely oriented to the plane of the magnets. The coil is energizeable for effecting a reciprocating motion of the magnets along a single fixed axis.
The above linear actuators are extremely effective and miniature. They can be used in a variety of situations. This is so especially where space, weight and low electric power consumption are desired. Despite their many advantages, however, there are certain limitations. One is that the armatures must move along a single path. Hence, the armatures cannot move in multiple directions.
U.S. Pat. No. 3,836,835 discloses a linear movement positioning system wherein an armature is movable along a single axis or a pair of coordinate axes. U.S. Pat. No. 3,904,900 discloses a pulse operated two-axes magnetic positioning device by which an object can be transferred in a first direction, a second direction which is not parallel to the first direction or in any direction between the first and second directions on a horizontal plane. These devices, however, accomplish the two-axes positioning by a plurality of conventional pulse operated electromagnetic motors.